1. Field of the Invention
The invention relates to document handling equipment including systems for feeding and transporting documents. The invention further relates to detecting the presence of staples, paper clips, and like foreign items in a stream of continuously-fed moving paper items in a document processing system.
2. Background Art
A typical system for feeding and transporting documents includes a feeder in the document feeding portion of the system, and a series of roller pairs or belts in the document transporting portion of the system. In the feeding portion of the system, the feeder acts to separate and feed documents singly, in order, from a stack. In the transporting portion of the system, the roller pairs and/or belts convey the documents, one at a time, through a track past other processing devices such as readers, printers, and sorters that perform operations on the documents. The feeder is typically a feed wheel, but may take other forms. Further, the components in the transporting portion of the system may take a variety of forms. Operations that depend on the position of the document are generally performed in the transport stage, or transporting portion of the system.
Typically, the document track has drive rollers and pinch rollers positioned along the document path to propel a document down the track. The document track sidewalls are usually rigid and non-movable. The document track is narrow and deep, typically with only the top portion of a document visible, or with no document visibility at all.
Workers in the art of high-speed document processing will be familiar with the problems which are caused when the documents to be processed include attachments such as staples and paper clips. These attachments are inevitable and unavoidable when the documents being processed include, for example, financial documents, checks, remittances, and the like.
In machines which are designed to feed, move and process document items at high speeds and rates, such attachments can be very destructive. For example, in a machine designed to read magnetically-encoded characters on bank checks, a single metal staple can destroy the magnetic air-gap read head which is required for such reading. Such an event may lead to costly repairs and down-time.
For these reasons, makers of document-processing machinery have sought to either eliminate staples and the like from the documents to be processed, or to detect their presence before they can do damage. For example, an existing financial document processor includes an electromagnetic staple-detect feature which scans each item as it is fed and moved, detects the presence of any metallic attachment, and stops the machine before the attachment can do damage.
The existing approaches for detecting staples and other metallic attachments have been successful; however, there are opportunities for improvement. For example, the detection mechanism may involve the use of complex and costly electromagnetic sensing heads, which typically operate by applying a significant magnetic field (by means of a permanent magnet) and then sensing changes in the applied field using a series of electrical sense coils. Because an attachment can be in any physical orientation, multiple sense coils in multiple orientations are usually required to ensure that all attachments will be sensed. Such sensing heads become both physically large and complex, and also very costly, if they are to perform well.
An alternative approach for detecting staples includes the provision of an energized or oscillating sense coil or coils, through the center of which the documents to be processed are passed. The presence of an attachment is sensed by variations in the magnetic field or oscillations of the sense coils, according to known principles. Such an approach suffers from the drawback that a sense coil must completely encircle the document and the track in which the document travels, hindering service and error-recovery attention. Such sensing approaches also tend to require complex and delicate signal-conditioning electronics to function reliably, and may also create problems of electromagnetic interference (EMI) or radio-frequency interference (RFI), which are subject to regulatory control and sanction.
For the foregoing reasons, there is a need for an improved approach to detecting staples, paper clips, and like foreign items in a stream of continuously-fed moving paper items that overcomes some of the limitations of existing approaches.